This application is a 35 U.S.C. 371 application of PCT/DE01/01720, filed May 8, 2001.
1. Field of the Invention
The present invention relates to a method for operating a fuel metering system of a direct-injection internal combustion engine, having a fuel supply container, at least one prefeed pump for pumping fuel out of the fuel supply container into a low-pressure region of the fuel metering system, a high-pressure pump assembly having at least two high-pressure pumps for pumping fuel out of the low-pressure region into at least one high-pressure reservoir, a control unit for regulating an injection pressure prevailing in the high-pressure reservoir, and having fuel injection valves for injecting fuel out of the high-pressure reservoir into combustion chambers of the engine.
The invention also relates to a fuel metering system of a direct-injection internal combustion engine, having a fuel supply container, at least one prefeed pump for pumping fuel out of the fuel supply container into a low-pressure region of the fuel metering system, a high-pressure pump assembly having at least two high-pressure pumps for pumping fuel out of the low-pressure region into at least one common rail, a control unit for regulating an injection pressure prevailing in the high-pressure reservoir, and having fuel injection valves for injecting fuel out of the high-pressure reservoir into combustion chambers of the engine.
The present invention further relates to a fuel metering system of a direct-injection internal combustion engine, which includes a fuel supply container, at least one prefeed pump for pumping fuel out of the fuel supply container into a low-pressure region of the fuel metering system, a high-pressure pump assembly having at least two high-pressure pumps for pumping fuel out of the low-pressure region into at least one high-pressure reservoir, a control unit for regulating an injection pressure prevailing in the high-pressure reservoir, and fuel injection valves for injecting fuel out of the high-pressure reservoir into combustion chambers of the engine.
Finally, the invention also relates to a control unit for a direct-injection internal combustion engine of this type.
2. Description of the Prior Art
Direct-injection internal combustion engines of the type referred to at the outset, with fuel metering systems of the type referred to at the outset, are known from the prior art, for instance in the form of engines with direct gasoline injection. The fuel metering system has a prefeed pump, typically embodied as an electric fuel pump, which pumps fuel out of a fuel supply container into a low-pressure region of the fuel metering system. A high-pressure pump assembly of the fuel metering system pumps fuel out of the low-pressure region at high pressure into a high-pressure reservoir. The high-pressure reservoir is embodied for instance as the distributor strip of a common rail (CR) fuel metering system. From the high-pressure reservoir, injection valves branch off, by way of which fuel can be injected from the high-pressure reservoir into combustion chambers of the engine. The injection valves are triggered by a control unit of the engine. The control unit further has the task of regulating the injection pressure, via a pressure regulating circuit, that prevails in the high-pressure reservoir. Increasing the injection pressure can be achieved by suitable triggering of the high-pressure pump assembly, or in other words by increasing the delivery of fuel to the high-pressure reservoir. Reducing the injection pressure can be achieved by suitable triggering of a control valve that branches off from the high-pressure reservoir, that is, by increasing the fuel outflow from the high-pressure reservoir, or by reducing the pumping capacity of the high-pressure pump. The control valve is embodied for instance as a quantity control valve (in the case of one-cylinder piston-type high-pressure pumps) or as a pressure control valve (in three-cylinder radial piston high-pressure pumps).
In internal combustion engines with four cylinders or fewer, or in internal combustion engines with a relatively small displacement, the high-pressure pump assembly as a rule includes only a single high-pressure pump. The pump can be embodied as a one-cylinder piston pump, for example, or as a three-cylinder radial piston pump. With one high-pressure pump, in engines with four cylinders or fewer or in engines with a relatively small displacement, a reliable supply of the requisite fuel quantity to the combustion chambers can be assured in all the operating states of the engine.
However, it has been found that in engines with a relatively large displacement or engines with six cylinders or more, reliable fuel supply can no longer be assured with only a single high-pressure pump. It is therefore known from the prior art for a fuel metering system to be divided into two independent fuel circuits. The independence of the fuel circuits fundamentally requires that there be two high-pressure reservoirs and two pressure regulating circuits, which must be triggered by the control unit and must above all be coordinated. Each of the fuel circuits has its own high-pressure pump, which is triggered via its own pressure regulating circuit. This kind of subdivision of the fuel metering system into two fuel circuits is known from the prior art for six-cylinder engines, in which case each fuel circuit is responsible for supplying the combustion chambers of three cylinders, and for eight-cylinder engines, in which case each fuel circuit is responsible for supplying the combustion chambers of four cylinders. The proposals known from the prior art for assuring reliable fuel supply to engines of relatively large displacement or engines with six or more cylinders, however, involve relatively complicated and expensive systematic solutions.
From German Patent Disclosure DE 198 23 639 A1, a common rail (CR) fuel metering system of the type described at the outset is known, with one prefeed pump and one high-pressure pump. From German Patent Disclosure DE 195 23 283 A1, a high-pressure pump for a fuel metering system is known. The described high-pressure pump can be embodied as either a radial piston pump, with three pump pistons disposed in a star pattern, or as an axial piston pump, with two pump pistons disposed parallel to one another. In the known high-pressure pump, the individual pistons are actuated via a common cam or eccentric drive. In other words, there is a fixed mechanical coupling among the individual pump pistons, which does not allow targeted actuation of individual pump pistons. Although the known high-pressure pump has a plurality of pump pistons, nevertheless it must be considered as a single high-pressure pump.
From other fields in automotive technology, especially from the field of brake systems and active suspension systems, pump assemblies with a plurality of pump pistons are known. For instance, from German Patent DE 40 41 800 C2, a two-piston pump, embodied as an axial piston pump, of an anti-lock brake system is known, with two pump pistons disposed parallel to one another. From European Patent Disclosure EP 0 448 836 A1, a reciprocating piston pump in a vehicle brake system, for pumping fluid, is known that is embodied as a radial piston pump with two diametrically opposed pump pistons. Finally, from German Patent Disclosure DE 40 27 794 A1, a radial piston pump is known for supplying energy to the vehicle hydraulic system (anti-lock system or ABS, traction control or ASR, active suspension control). It is a common feature of all these pump assemblies that there is a fixed mechanical coupling among the individual pump pistons, and targeted actuation of individual pump pistons is not possible, so that all these pump assemblies have to be considered as single pumps.
The object of the present invention is, in a structurally simple and as inexpensive as possible a way, to assure reliable fuel supply particularly in engines with four or more cylinders or in engines of large displacement.
To attain this object, the invention proposes, on the basis of the method of the type defined at the outset, that the fuel metering system has one fuel circuit for metering fuel into all the combustion chambers of the engine, and all the high-pressure pumps are disposed in the fuel circuit, and that all the high-pressure pumps are triggered independently of one another via a common pressure regulating circuit.
According to the invention, the fuel metering system is accordingly not subdivided into a plurality of fuel circuits; instead, only one fuel circuit is provided for metering fuel to all the combustion chambers of the engine. All the high-pressure pumps of the high-pressure pump assembly are disposed in this fuel circuit. The fuel metering system of the invention preferably has two high-pressure pumps. The high-pressure pumps used can be embodied as standard pumps, such as one-cylinder piston pumps or three-cylinder radial piston pumps, of the kind known per se from the prior art. The control unit of the fuel metering system triggers all the high-pressure pumps independently of one another via one common pressure regulating circuit. Only a single high-pressure reservoir is disposed in the fuel circuit, and its injection pressure can be regulated by only a single pressure regulating circuit. As a result, the method can be achieved in an especially simple, economical way.
Also with the method of the invention, a reliable supply of fuel to the combustion chambers, especially in engines of relatively large displacement or engines with four or more cylinders, can be assured.
Because the high-pressure pumps pump into a common high-pressure reservoir, simple regulation of the injection pressure that prevails in the high-pressure reservoir is attainable with only a single pressure regulating circuit. Only in the case of the end stages for triggering the high-pressure pumps do two of them have to be provided. At the same time, in asymmetrical ignition sequences, the method of the invention avoids a complex structure of the fuel metering system.
In an advantageous refinement of the present invention, it is proposed that the high-pressure pumps are triggered parallel to one another. In other words, the high-pressure pumps are triggered in synchronized fashion and execute an intake stroke and a pumping stroke simultaneously.
Alternatively, in another advantageous refinement of the present invention, it is proposed that one or more first high-pressure pumps are triggered oppositely from one or more second high-pressure pumps. The first high-pressure pumps and the second high-pressure pumps execute the intake stroke and the pumping stroke in staggered fashion; that is, when the first high-pressure pumps are in the intake stroke, the second high-pressure pumps are in the pumping stroke; conversely, when the high-pressure pumps are in the pumping stroke, the second high-pressure pumps are in the intake stroke. The advantage of this refinement is that a marked reduction in the different pressure levels of successive injections can be attained, since the replenishment is distributed uniformly. A further advantage is the possibility of simple diagnosis of the high-pressure pumps, because the course of the injection pressure prevailing in the high-pressure reservoir is monitored.
For triggering by the control unit in a way that is economical in terms of resources, it is proposed in a preferred embodiment of the present invention that the high-pressure pumps are triggered with the same triggering time. The triggering time is accordingly calculated in the control unit only once for all the high-pressure pumps of the fuel metering system. The triggering of the individual high-pressure pumps is then effected via a switchover device, which switches over between the first high-pressure pumps and the second high-pressure pumps at the appropriate instance or at the appropriate angular position of the engine crankshaft. In this way, with the same triggering time, the first high-pressure pumps and the second high-pressure pumps can be triggered in alternation.
As a further way of attaining the object of the present invention, based on the fuel metering system of the type defined at the outset, it is proposed that the fuel metering system has one fuel circuit for metering fuel into all the combustion chambers of the engine, and all the high-pressure pumps are disposed in the fuel circuit, and that the control unit includes one pressure regulating circuit for all the high-pressure pumps, and the high-pressure pumps are triggerable independently of one another via the pressure regulating circuit.
In a preferred refinement of the present invention, it is proposed that the high-pressure pump assembly has two high-pressure pumps.
In a preferred embodiment of the present invention, it is proposed that the control unit triggers the high-pressure pumps parallel to one another. As an alternative, it is proposed that the control unit triggers one or more first high-pressure pumps oppositely from one or more second high-pressure pumps.
Advantageously, the control unit triggers the high-pressure pumps with the same triggering time.
In an advantageous refinement of the present invention, it is proposed that the engine has at least six cylinders.
In a preferred embodiment of the invention, the fuel metering system has two high-pressure reservoir regions, which communicate with one another via a pressure equalization line. By means of the pressure equalization line, the two high-pressure reservoir regions are combined into a common high-pressure reservoir.
Finally, based on the control unit of the type defined at the outset, as still another way of attaining the object of the present invention, it is proposed that the fuel metering system has one fuel circuit for metering fuel into all the combustion chambers of the engine, and all the high-pressure pumps are disposed in the fuel circuit, and that the control unit triggers all the high-pressure pumps independently of one another via a common pressure regulating circuit.
In an advantageous refinement of the present invention, it is proposed that the control unit triggers the high-pressure pumps parallel to one another. Alternatively, it is proposed that the control unit triggers one or more first high-pressure pumps oppositely from one or more second high-pressure pumps. Advantageously, the control unit triggers the high-pressure pumps with the same triggering time.
Realizing the method of the invention in the form of a control element which is provided for a control unit of a direct-injection internal combustion engine is of particular significance. A program is stored in memory in the control element that can be run on a computer, especially a microprocessor, and is suitable for performing the method of the invention. In this case, the invention is accordingly realized by a program stored in memory in the control element, so that this control element having the program is as representative of the invention as the method for whose execution the program is suited. As the control element, an electrical storage medium can in particular be used, such as a read-only memory or a flash memory.